Electrical Properties of High-Quality Stannic Oxide Crystals

Abstract

Single crystals of the wide bandgap semiconductor stannic oxide, SnO2, have been grown and studied electrically. A chemical vapor deposition technique using chlorine transport, no inert carrier gases, and low pressure has been used to grow stannic oxide crystals of higher purity and with almost an order-of-magnitude higher low-temperature Hall mobility, 8800 cm2/V sec at 80°K, than have previously been available. Measurements of Hall mobility, carrier concentration, and resistivity have been made between 20 and 625°K on crystals with room-temperature carrier concentrations between 8×1015 and 2×1018 cm−3. The effects of the crystal anisotropy on these measurements have been investigated and found to be small (all results reported are for the a direction). A donor level ∼35-meV deep due to antimony and another level ascribed to oxygen vacancies at ∼140 meV have been observed. Polar optical mode scattering with a dominant characteristic temperature of 1080°C is the main carrier scattering mechanism above 250°K. Below 250°K acoustic deformation potential scattering dominates. Ionized impurity scattering is eventually important in all samples as the temperature is lowered. A polaron effective mass of 0.39 me has been found consistently in the analyses of the data. A technique of fabricating good Schottky barriers on SnO2 has also been developed and used to measure the net donor concentration in samples. The agreement found between these measurements and Nd from Hall measurements indicates that shallow trapping is not a problem in these crystals.

Sources of Electrical Conductivity inSnO2

“…The calculated barrier in this case is 2.2 eV. We conclude that H O is stable enough to explain the observed unintentional n-type conductivity in SnO 2 [5,8]. Indeed, an increase in carrier concentration has been observed upon exposure to moist air or H 2 [12,13].…”

“…However, as-grown SnO 2 exhibits n-type conductivity even when not intentionally doped [5][6][7][8]. We therefore focus specifically on hydrogen, which is commonly present in (and difficult to exclude from) the various growth and processing environments.…”

“…Asgrown SnO 2 generally exhibits high levels of unintentional n-type conductivity [5][6][7][8]. Because this conductivity varies inversely with the oxygen partial pressure, it has been commonly attributed to the presence of native point defects, in particular, to oxygen vacancies [3,[5][6][7].…”

Grain-boundary-limited transport in semiconducting SnO2 thin films: Model and experiments

“…͑4͒. The mobilities are typically an order of magnitude lower than the values measured in single-crystalline samples of similar carrier density, 10,11 which already points to the importance of the grain boundaries in limiting the carrier transport. First, we will describe the results for the respective samples, mainly in terms of the energy band diagrams.…”

Rational design of SnO2-based electron transport layer in mesoscopic perovskite solar cells: more kinetically favorable than traditional double-layer architecture

“…Actually, many attempts have been performed in order to make ETL kinetically more favorable, e.g., surface modifications, nanostructure tailoring, and the utilizations of alternative materials with better optoelectronic properties [16][17][18][19][20][21][22][23]. Compared with TiO 2 , SnO 2 is chemically stable as well and, more importantly, its charge mobility is almost two orders of magnitude higher than that of TiO 2 [11,24]. On the other hand, the photocatalytic activity is less pronounced due to a higher band gap of~3.8 eV for SnO 2 , which is favorable to the long-term stability of PSCs [25].…”